Pythium is a genus of oomycetes, water moulds that look like fungi but are more closely related to brown algae. Several species infect cannabis roots, including P. myriotylum, P. dissotocum and P. aphanidermatum. They spread by swimming zoospores, so they thrive wherever roots sit in water: deep water culture, recirculating systems and overwatered pots. They also cause damping-off of seedlings and cuttings.
In practice
Infected roots turn brown, soft and slimy, and the outer root tissue slips off, leaving the inner strand. Above ground the plant wilts in the heat of the day, yellows and stalls, despite a full reservoir. Warm nutrient solution above roughly 24-26 °C (75-79 °F), low dissolved oxygen and stagnant water favour it. Prevention is cool, well-oxygenated solution, clean equipment, and either a dedicated beneficial-microbe reservoir or a fully committed sterile one. Fungus gnat larvae can carry it in media.
Don't confuse with
- Fusarium: a true fungus that often causes wilt and brown vascular streaks in the stem.
- Tea-stained roots: brown from additives but firm, with white tips.
- Overwatering in soil: low oxygen without slime or root sloughing.
DWC (deep water culture) suspends a plant's roots in an aerated nutrient solution, typically in a bucket with a net pot lid and an air stone.A recirculating (closed) system returns drained nutrient solution to the reservoir to be reused, saving water and nutrients but needing more monitoring and sanitation.Overwatering is watering so often that the medium stays saturated, starving roots of oxygen, which causes drooping, slow growth and root disease.The collapse of seedlings or cuttings when soil-borne pathogens such as Pythium, Rhizoctonia solani and Fusarium rot the stem at the soil line.A seedling is a young cannabis plant from emergence of the cotyledons until it has several sets of true leaves, typically the first 2-3 weeks.Pest and disease prevention by changing how the crop is grown, such as humidity, airflow, spacing, watering and cultivar choice, so pests and pathogens struggle to establish.A beneficial-microbe reservoir deliberately inoculates hydroponic solution with helpful bacteria and fungi so they occupy the root zone before pathogens can; GenetixBay prefers this approach.Small dark flies of the genus Bradysia (family Sciaridae) whose larvae live in wet growing media, feeding on fungi, organic matter and young roots.Decay of roots by pathogens such as Pythium, Fusarium, Rhizoctonia or Phytophthora, usually triggered by low oxygen, heat and waterlogging around the roots.A soil-borne fungal disease, chiefly Fusarium oxysporum, that blocks water-conducting tissue, causing one-sided yellowing, wilting and brown streaks inside the stem.A slimy community of microbes stuck to surfaces in a matrix they secrete; in hydro, it coats lines, reservoirs and roots and can shelter pathogens.
